For horror fans, Eli Roth and cannibal movies both bring a set of expectations that are met by “The Green Inferno,” modern shockmeister Roth’s first feature since 2007’s “Hostel II.” The cannibal genre that came and went in the seventies and eighties was known less for the quality of filmmaking than its sheer indulgence in graphic violence, which generally involved naive Westerners running into lethal trouble with flesh-hungry tribes. “The Green Inferno” follows suit, delivering oodles of the unsettling that helped give rise to the infamous “torture porn” moniker in Roth’s earlier movies. Unfortunately, the unbridled shock value isn’t matched by a similar investment in other ingredients that might have made this low rent B-movie worthwhile.

Still, “The Green Inferno” reflects its director’s giddy attraction to turning disgusting imagery into escapism, and with so many possibilities offered up by the genre, it’s no wonder that a sequel is already lined up. Ironically, however, the movie’s stronger aspects lie with the story. Co-written by Roth and Guillermo Amoedo, the basic premise finds Barnard college girl Justine (Lorenza Izzo), the privileged daughter of a high-powered lawyer for the U.N., drawn to participate in an activist group’s attempt to prevent deforestation in the Amazon rainforest. In concept alone, “The Green Inferno” takes a clever jab at the brainless posturing that afflicts certain activist groups with hidden agendas, but the idea plays out with a juvenile sensibility on par with the grotesque chaos.

Though there’s plenty of buildup, as Justine learns of third world terrors from the ivory tower of her college classroom and gradually develops the urge to take action, once the cannibals enter the picture “The Green Inferno” drops most of its thematic depth in favor of routine bloody mayhem. Led by the ostensibly good-natured team leader Alejandro (Ariel Levy), the group heads to Peru and successfully prevents bulldozers from knocking down a handful of trees, only to endure a plane crash on the way out and wind up immediately in the captivity of the natives they were trying to protect.

From that point forward, the maiming and mass tribal consumption begins in earnest, as Alejandro, Justine and a handful of other survivors hover in the corner of a wooden prison watching helplessly as their captors take their first victim. In terms of disturbing imagery, the initial cannibal feast doesn’t disappoint: Aided by renowned makeup artist Greg Nicotero, Roth delivers a terrifically gross sequence in which one unfortunate screaming man gets maimed to death and devoured piece by piece.

But if that’s main dish “The Green Inferno” aims to serve, it lacks further bite. No other death scene can match this first one; in fact, by Roth’s standards, the sicker parts are relatively coy. Most of the running time involves the English-speaking characters chatting amongst each other and fretting over what to do about their predicament. The cannibals maintain a similarly one-note quality that makes it hard to take the threat seriously (although a fleeting glimpse of them going through the practical motions of preparing their meal provides a briefly satisfying contrast to the carnage). While Justine latches on to a potentially sympathetic young girl from the tribe, the rest of natives are rendered as cartoonish villains largely indistinguishable from one another. Even the two-menacing leaders remain silly, half-baked constructions — an elderly woman intent on enacting a depraved female circumcision ritual on the American women and wide-eyed, rock-wielding executioner who barks orders and shows no mercy.

The prisoners have a lot more screen time, but not much depth. Pop singer Sky Ferreira, as one of the other clueless activists, spends the majority of her scenes glaring in vain at everyone around her. Levy, as the alleged know-it-all who dragged everyone into this mess, mainly just scowls in a feeble bid to look like he’s cooking up a plan. Only the gradually more assertive Izzo generates some semblance of credibility as she adjusts to the conundrum and finally takes action, but the payoff lacks sufficient imagination to follow through on her transition.

That’s the greatest frustration that comes out of enduring “The Green Inferno”: Even though it celebrates the unsettling power of showing psychotic behavior enacted on defenseless foreigners, Roth never comes up with anything as inventively terrifying as the murders found in his earlier movies. Sure, one character abruptly commits suicide and another gets torn to bits by a mob, but given the expectations at hand, these moments suffer from a lack of imagination as well as the ability to complicate the uneasiness. Instead, they play like cheap, campy gimmicks that simplify the material.

Unlike last year’s Roth-produced disaster movie “Aftershock” (directed by Nicolas Lopez, who’s attached to handle the “Green Inferno” sequel), the conceit levels off at the end of the first act rather than building to a bigger moments with the ability to deepen its ideology or willingness to indulge in terrifying extremes. Despite an apparent commitment to generating bonafide horror, “The Green Inferno” actually tends more toward a sloppy comedic sensibility. One throwaway scatological gag involving a captive who gets the runs wouldn’t be out of place in the vignette-based spoofs directed by the Zucker brothers.

Of course, one can’t fault “The Green Inferno” for attempting to provide satiric insight, and the punchlines of its closing scenes efficiently bring the social commentary embedded in the plot full circle. Its cynical attitude toward blind posturing in favor of murky causes provides ample fodder for discussion. “There’s always a non-violent way to make a point,” one of the activists announcing early on, and the movie eventually replies with a dour rebuke. Yet “The Green Inferno” isn’t made well enough to make that debate count for anything. Its knowingly racist depiction of the demented tribe might be well-positioned to comment on the danger of not treating real world suffering with a careful eye, but in that regard, the movie’s a victim along with its subjects.

Criticwire grade: C-

HOW WILL IT PLAY? Too graphic and niche-oriented for widespread theatrical play, “The Green Inferno” is well-positioned to do perform well on VOD and on the midnight movie circuit in the hands of a genre label willing to play up its appeal to committed horror enthusiasts.